1. Field of the Invention
The present invention relates to solid-state imaging apparatus.
2. Description of the Related Art
As a solid-state imaging apparatus for an image scanning apparatus like a copying machine and a scanner, there is a solid-state imaging apparatus that includes photodiodes for reading out different color components and holding capacitors corresponding to respective photodiodes as shown in FIG. 1 of Japanese Patent Application Laid-Open No. 2006-211363 (Patent Document 1).
Japanese Patent Application Laid-Open No. 2006-211363 discloses the solid-state imaging apparatus that has one common output line, whereas Japanese Patent Application Laid-Open No. H06-204445 (Patent Document 2) proposes the solid-state imaging apparatus that can output a signal for each of the color components as shown in FIG. 4. Since the arrangement disclosed in Japanese Patent Application Laid-Open No. H06-204445 outputs signals through a plurality of common output lines in parallel, it can reduce the time for reading out signals as short as that took by the arrangement disclosed in Japanese Patent Application Laid-Open No. 2006-211363 divided by the number of the common output lines.
When performance improvement such as improvement in an S/N ratio is required, an arrangement having an amplifying circuit provided for a vertical transferring unit, which operates at a low-speed, for amplifying signals in a narrow band to achieve low noise is utilized, as shown in Japanese Patent Application Laid-Open No. 2008-54246 (Patent document 3)and Japanese Patent Application Laid-Open No. 2008-60949 (Patent Document 4).
It is known, however, that an artifact according to the light intensity of the input image called smear may occur due to the above-mentioned amplifying circuit in the arrangements disclosed in Japanese Patent Application Laid-Open No. 2008-54246 and Japanese Patent Application Laid-Open No. 2008-60949. Other than the mechanism of causing the artifact shown in the above-mentioned documents, an artifact may be caused by such a mechanism in which an excess current that is generated when a signal from the previous stage is sampled in the holding capacitor changes a source bias with its source impedance, and the change in the source offsets the signal value from each column. Also, when a source follower circuit is used as the amplifying circuit in a pixel, the bias on the current source transistor of the source follower circuit is pressed by the signals, resulting in the current change, which may offset the signal value from each column. Here, the ‘smear’ may appear white (floating component) or black (sinking component) to the light intensity according to the place it is generated and the polarity of the signal.
The present invention has been adapted in view of the above circumstances and has an object of enabling the reduction of degrading image quality due to artifacts such as smear.